Method and apparatus for chipping logs



0 United States Patent 11113,545,510 [72] Inventors Thomas P. Bush, Jr. 5 m- Cited 133 Red Oak Road, Birmingham, Alabama UNITED STATES PATENTS 35206: Samuel E. Gram, 7254 Sandy Bluff Drive, 3,371,693 3/1968 Voelskow 144/172 Jacksonville, Florida 3221] Appl. No. 763,521 Filed Sept. 30, 1968 Patented Dec. 8, 1970 METHOD AND APPARATUS FOR CHIPPING LOGS Primary ExaminerGerald A. Dost Attorney-Newton, Hopkins & Ormsby ABSTRACT: A method and apparatus for chipping logs PATENTEU DEC 8 I970 sum 1 [1F 2 PATENTED 05a 8 I970 SHEET 2 OF 2 LOG OUT 'LOG IN METHOD AND APPARATUS FOR CHIPPING LOGS BACKGROUND OF THE INVENTION wood chips debarked logs fed to the log chipper. These prior art log chipper assemblies have been quite massive machines thereby requiring a large space in which to operate and have usually had the chipping blades thereof directly driven by a prime mover, such'as an electric motor, through direct drive gear reducers. For example, when an electric motor was used, 500 to 2,500 horsepower, was required to drive the log chipper. Because the speed of thechipper was not allowed to appreciably vary, these prior art chippers required a prime mover which was extremely powerful in order to handle the peak load encountered at the start of the chippingof a log.

In these prior art machines the initial cost of the 500 to 2,500 horsepower motors was quite high, and the cost of electrical cables, fuse boxes, starting panels, etc., for the installation of such motors was also quite high. Moreover, since most power companies charge not only according to the amount of power consumed, but also according to the peak load or demand rate, the cost of operating such a 500 to 2,500 horsepower motor was also high.

Due to the fact that thernotor was directly geared to the chipper blades of such log chipper assemblies, the shock normally encountered when a log is initially fed into the log chipper and the change in torque associated with the chipper as the log is being chipped was transmitted directly to the mo tor. This resulted in extremely high maintenance and operating cost when using the prior art log chipper assemblies.

SUMMARY OF THE INVENTION These and other problems associated with the prior art log chipping assemblies are overcome by the invention disclosed hereby by utilizing a log chipper assembly which includes a heavy flywheel mounting the chipper blades which is capable of storing large amounts of rotational kinetic energy. This flywheel is electromagnetically connected indirectly to the prime mover rotating the flywheel and chipper blades. The electromagnetic connection between the flywheel and the prime mover is accomplished by the use of an eddy-current clutch coupling. By such an arrangement, the horsepower requirements of the motor are reduced approximately twothirds to four-fifths of the horsepower requirements of the prior art log chipping assemblies. In other words, through the arrangements of the chipper assembly disclosed herein, only a 200 to 500 horsepower motor is required to perform substantially the same chipping operation as heretofore performed by prior art log chipping assemblies having 500 to 2,500 horsepower motorsflhus, the expense of installation and operation of the log chipper assembly of the invention disclosed herein is appreciably less than that of the prior art log chippe assemblies.

Accordingly, it is an object of the invention disclosed herein to provide a log chipper assembly which is inexpensive to manufacture, durable in structure, and efficient in operation.

Another object of the invention is to provide a log chipper assembly in which the horsepower requirements for operating the assembly are appreciably reduced.

Another object of the invention is to provide a log chipper assembly in which the shock of the chipper blades as they engage the logs will not be transmitted, to any appreciable extent, directly back to the motor or prime mover.

Briefly described, the apparatus of the invention includes a log chipper having a plurality of radially spaced chipper blades carried by a heavy flywheel; a prime mover, such as an electric motor; and an eddy-current clutch coupling connecting the motor to the flywheel of the log chipper through a gear reducer. The clutch electromagnetically connects the output shaft of the motor with the input shaft of the log chipper so that the flywheel of the log chipper can be rotated at a rated r.p.m. prior to the insertion of a debarked log into the log chipper. This stores a large amount of rotational kinetic energy in the flywheel. The motor is driven at a relatively constant speed and the kinetic energy of the flywheel is utilized to absorb the initial shock when the debarked log is fed into the log chipper. The clutch allows slippage between the motor and the flywheel to give the motor an extended period of time while the log is being chipped to restore the flywheelof the log chipper to its initial rpm. and thus its initial kinetic energy prior to the next log being chippedl. This is because much less energy is utilized after the initial peak load encountered when the log is first inserted into the chipper assembly due to the taper of the log.

Other objects, features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein like charactersof reference designate corresponding parts throughout and in. which:

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF ILLUSTRATIVE EMBODIMENT Referring now in detail to the embodiment chosen for the purpose of illustrating the apparatus of the invention as shown in FIG. 1, the log chipper assembly includes a log chipper 10, a gear reducer 20, an eddy-current vclutch coupling 30 and an electric motor 40. The chipper 10., gear reducer 20, coupling 30, and motor 40 are arranged in tandem with their respective shafts in alignment. A support frame 50carries the elements of the log chipper assembly so that the motor 40 drives the eddy-current clutch coupling 30 which in turn drives the gear reducer 20 which in turn drives the log chipper 10.

In more detail, the log chipper 10 includes a hollow, rectangular log chipper housing 11 which is open in its upper and lower edges, and which is provided with feet 12 by means of which the housing 11 is supported in an elevated position. The housing 11 defines a chipping chamber therein into which logs to be comminuted are fed. The upper edge portion of the housing 11 is provided with a pair of spaced opposed bearing blocks 13 positioned on opposite sides of the chamber 13 and form journals for chipper shaft 14. 1

Between the bearing blocks 17, shaft 14 mounts for rotation therewith a relatively large, heavy, flywheel 15. The lower periphery of the flywheel 15 protrudes into the chipping chamber and the remainder of the flywheel 15 is encased by a pair of semidisc-shaped casings 16 to provide inspection of the chipping chamber and the flywheel 15; The casings 16 are received over the upper periphery of the flywheel 15 so that the flywheel 15 is rotatably mounted therein. The casings 16 are supported along their lower portions on the housing 11. Mounted on the front face of the flywheel 15 are a plurality of radially spaced chipper blades 18 of conventional design. Therefore, it will be seen that, upon rotation of the flywheel 15, the chipper blades 18 will successively engage and corn minute logs fed into and through the chamber 13 into chips. Such a log is indicated in broken lines in FIG. 1 and designated by the reference numeral 19.

Since it is important that the flywheel possess a large amount of kinetic energy when being rotated, the flywheel is made approximately percent thicker than the conventional flywheels normally found in log chippers. Since the amount of kinetic energy stored in the rotating flywheel 15 is directly proportional to the mass, increasing the thickness of the flywheel 20 percent also increases the kinetic energy storage capabilityof'the flywheel 20 percent. When the flywheel 15 is rotated at a given r.'p.m., a specific amount of kinetic energy is stored therein. A portion of this stored kinetic energy, is used to absorb the shock load normally subjected to the log chipper as a log is initially fed therein. After the initial shock load sub jected to the log chipper has been overcome, the flywheel 15 may be returned to its initial r.p.m., by the motor 40 because the normal chipping load is substantially less than the shock load.

The, logs 19 are successively fed end to end into the chipping chamber and against the chipper blades 18 through a hollow throat member 21 defining a passage therethrough in communication with the chipping chamber. The axis of the throat member 21 is located at an angle with respect to the axis of the flywheel 15 as in conventional log chippers so as to cause the blades 18 to engage the front edge or corner of the log 19 and urge it inwardly as the log 19 is comminuted by the chipper blades 18 A suitable conveyor 22, shown in broken lines, feeds the logs 19 through the throat member 21 and into the chipping chamber. The wood chips comminuted from the log 19 pass downwardly out of the open bottom of the chipping chamber and are conveyed away in conventional manner for use in the paper manufacturing industry. I

The frame 50 mounts the gear reducer 20, the eddy-current clutch coupling 30, and the motor 40 is an elevated position above the lower portion of the housing 11 so that. the shafts thereof are aligned with each other and with the chipper shaft 14. The outer or rear end of the chipper shaft 14 is provided with a butt mounted disc 23 of a shear coupling C1 for connection with the gear reducer 20. The gear reducer 20 includes a driving shaft 28 extending from one side thereof and a driven shaft 29 extending from the other side thereof. The driven shaft 29 mounts a complimentary disc 24 of the shear coupling C1 on the outer end thereof and is connected with the disc 23 in conventional manner through bolts and nuts (not shown) so that rotation of the driven shaft 25 of the gear reducer 20 serves to rotate the chipper shaft 14 and the flywheel 15.

The driving shaft 28 of the gear reducer 20 is provided at its outer or rearwardly extending end with disc 27 of the shear coupling C2 for connection with the eddy-current clutch coupling 30. The eddy-current clutch coupling is provided with an input shaft 31 and an output shaft 29. The output shaft 29 is provided with a complimentary disc 28 to the disc 27 and is connected thereto by nuts and bolts (not shown) so that rotation of the output shaft 29 of the eddy-current clutch coupling 30 rotates the driving shaft 28 of the gear reducer 20 and thus the flywheel 15 of the log chipper 10.

In like manner, the input shaft 31 of the eddy-current clutch coupling is provided with a disc 32 of a shear coupling C3 for connection with the electric motor 40. The electric motor includes a drive shaft 34 which is provided on the forwardly extending end thereof a complimentary disc 33 which is joined with the disc 32 of the shear coupling C3 by nuts and bolts (not shown) so that rotation of the shaft 34 rotates the input shaft 31, of the eddy-current clutch coupling. it will be under'stood by those skilled in the art that the juxtaposed discs 23 and 24, 27 and 28, and 32 and 33 are joined by the nuts and bolts (not shown) in conventional manner so that, upon a substantial overload of any of the shear couplings C1C3, the bolts will shear and the machinery will not be injured.

The gear reducer 20 is of conventional design with the driving shaft 28 being geared to the driven shaft 25 through a con ventional gearing arrangement. The gear reducer 20 is preferably a 3 to 1 gear reducer whereby the driven shaft 29 rotates at one-third the speed of the driving shaft 26.

The eddy-current clutch coupling 30 is a stationary field, liquid-cooled, coupling having a squirrel cage induction drum on the input shaft 31 and a toothed rotor on the output shaft 29. This arrangement provides an electromagnetic connection between the input shaft 31 and the output shaft 29 but has no mechanical connection therebetween. Such a clutch coupling is manufactured by the Dynamatic Division of Eaton Yale and Towne, Inc. of Kenosha, Wis., under the trade name MAG- NAPOWER. Such a coupling 30 is provided with a feedback generator 35 which is driven from the output shaft 29 by an endless timing belt 36. The feedback generator 35 generates a current proportional to the speed'of shaft 29 and this current constitutes a signal for modulating the excitation current from a control unit U furnished with the coupling 30 by the manufacturer for automatically maintaining a substantially constant torque output on the shaft 29. A plurality of field coils electromagnetically connect the input shaft 31 and the output shaft 29 so that the control unit U can maintain the output torque for the shaft 29 by selectively exciting the field coils. Less than 400 watts of field excitation power is required to give complete regulation of the output torque of the output shaft 29 and since the control unit U is of conventional design and furnished by the manufacturer, the exact details of the circuit of the control unit are not depicted in the drawings.

The motor or prime mover 40 is shown as an electric motor, however, it is understood that other types of prime movers may be used for driving the eddy-current clutch coupling. The particular motor 40 shown is a squirrel cage induction motor. It will be understood that since there, is no mechanical linkage between the motor 40 and the log chipper l0; i.e., between output shaft 29 and input shaft 31 of the eddy-current clutch coupling 30; any momentary peak loads will not be transmitted directly to the motor 40.

By the arrangement described above, results comparable to those achieved by the prior art can be achieved using a motor 40 of approximately one-half to one-fifth the horsepower of the prior art motors associated with a log chipper. This is partly due to the fact that no high starting torques are imposed directly on the motor 40, and partlydue to the fact that the peak load normally encountered when the butt'end of a log is initially fed into the log chipper 10 is absorbed in a largepart by the eddy-current clutch coupling 30 in conjunction with the rotational kinetic energy in the flywheel 15.

Since most prime movers, especially electric motors, are primarily constant speed devices, the motor 40 is started while the field coils in the eddy-current clutch coupling 30 are not energized. Therefore, the output shaft of the coupling 30 will not be rotated while the input shaft 31 is rotated by the motor 40. After the motor 40 has attained its operational speed, the field coils of the coupling 30 are energized so as to cause the toothed rotor of shaft 29 to be pulled around by the eddy-currents created by the combination of the field coils and the squirrel cage induction drum mounted on shaft 31. Once the field coils of the eddy-current clutch coupling 30 are energized, it takes a relatively short time for the output shaft 29 to come up to speed and bring the flywheel 15 up to its rated r.p.m. The control unit U is so arranged that when the shaft 29 is up to speed, the output shaft29 is rotating at approximately 1,750 rpm. when the input shaft 31 is rotating at approximately 1,800 rpm.

Because the motor 40 operates most efficiently at its rated rpm, the undesirable characteristics exhibited by a prior art prime movers connected directly to the flywheel 15 are eliminated.

The eddy-current clutch coupling 30 allows the rotational speed of the flywheel 15 to be reduced when an overload is encountered or when a log first enters the chipper 10 without transmitting this speed reduction directly to the motor 40. Therefore, the motor 40 continues to operate at substantially its rated r.p.m. and the flywheel 15 is allowed to slow down so that the kinetic energy possessed by the flywheel 15 can be 'used to absorb the overload on the log chipper 10. The

flywheel 15 will regain its initial r.p.m. while the log is being chipped and before the next log enters the chipper 10.

The absorption of the overload on the log chipper can be best understood by referring to the graphs of FIG. 2 wherein the power required at the chipped is plotted in a dotted line graph while the power output of the motor is plotted in a solid line graph. The graphs are: appropriately marked tos how the point at which the log is started, normally butt end first, and where the log chipping operation is completed. When the butt end of the logis fed intothe chipper 10, the power requirements are quite high for a very short period of time. The eddycurrent clutch coupling 30 allows the flywheel to slow down and the output shaft 29 slip with respect to the input shaft 31 so that the motor 40 can maintain its rated r.p.m. By allowing the flywheel 15 to slow down, the kinetic energy possessed by the flywheel, when rotating at its initial r.p.m., is used to supply the additional power needed at the log chipper to handle peak or initial shock load exerted on the chipper 10.

it will also be noted from the graphs that once this relatively short peak load is overcome, the horsepower required to finish the chipping operation is substantially less than the rated horsepower of the motor 40. The motor 40 continues to operate at its maximum rated horsepower for a period of time after the peak load is reduced in order to restore the flywheel 15 to its initial r.p.m. The extra horsepower put into the log chipper 10 over that required to chip the log therein is used to restore the flywheel 15 back to its initial r.p.m. This, then, makes possible the use of the substantially reduced horsepower motor 40.

It will be obvious to those skilled in the art that any variations, substitutions and modifications may be made in the embodiment herein chosen forthe purpose of illustrating the invention without departing from the scope thereof as defined by the appended claims.

We claim:

1. A log chipper drive assembly for driving a log chipper having rotatable, radially spaced blades against which logs to be chipped are fed and a chipper shaft operatively connected to said blades for rotating said blades as said chipper shaft is rotated; said drive assembly including:

a prime mover having a drive shaft; and,

an eddy-current clutch. coupling having an input shaft and an output shaft, said output shaft electromagnetically coupled to said input shaft and mechanically connected to said chipper shaft to rotate said blades, and said input reducer having a driving shaft and a driven shaft, said driven a shaft mechanically connected to said driving shaft for rotation thereby and operatively connected to said output shaft of said coupling for rotation thereby.

4. The structure defined in claim 1 wherein the prime mover is an electrical, squirrel cage, induction motor.

5. The structure defined in claim 1 wherein said output and input shafts of said eddy-current clutch coupling, said driving and driven shafts of said gear reducer are in alignment and said chipper shaft and said prime mover drive shaft are aligned therewith, the adjacent associated shafts being connected together by shear couplings.

6. A method of comminuting logs: into chips with a log chipper having a heavy flywheel carrying a plurality of chipper blades which engage and comminute the logs comprising the steps of:

rotating a drive shaft at a substantially constant speed; and

electromagnetically connecting the drive shaft to the flywheel to selectively'rotatethe flywheel.

7. A method as set forth in claim 6 wherein the step of electroma netically connectin the flywheel with the drive shaft inclu es allowing the flyw eel to slow down with respect to the drive shaft when the load on the chipper blades exceeds the power output from the shaftshaft to permit the kinetic energy of the flywheel to absorb the overload on the drive shaft. 

